In the manufacture of bakery products, such as bread, rolls, and the like, the products are typically baked, and are thereafter cooled. Particularly in the case of bread, the next manufacturing step may comprise slicing. Ultimately, the bakery products are almost always wrapped, usually in a film bag, which serves to protect the products during transportation from the bakery to the consumer, and thereafter to preserve the freshness of the products until they are finally consumed.
The use of twist ties as the closure mechanism for the film wrappers of bakery products is advantageous in that it allows repeated opening and reclosing of the wrappers as the products are gradually consumed. U.S. Pat. No. 4,907,392 granted Mar. 13, 1990, to Knudsen, which is incorporated herein by reference as if fully set forth herein, discloses a Machine for Applying Twist-Type Ties to the film wrappers of bakery products. The present invention comprises an apparatus for applying twist ties which is similar in some respects to the Knudsen device, but which is faster, more accurate, and more reliable in operation. The apparatus of the present invention is an "on-demand" device for applying twist ties as air-tight closures to bagged bakery products in high-speed production line conditions.
The apparatus is unique in its flexibility to satisfy a wide variety of production situations, while requiring minimum maintenance. This flexibility has several sources:
1. The apparatus has no mechanical connections to its associated bagging machine. There is, however, one simple electrical connection for an interlock necessary to enable coordination between the bagger and the apparatus of the present invention.
2. Timing is controlled by a Programmable Logic Controller (PLC) to 1/100 second accuracy.
3. The PLC enables available fault logic unachievable in any mechanical machine, thus guaranteeing good ties with every tying cycle.
4. The apparatus can be easily and quickly moved from one bagger to another, with little or no adjustment required.
5. The apparatus can tie products faster than any machine available, because it makes no reciprocal motions--all motion is forward. But it can also tie slowly. The apparatus has been production tested at conveyor speeds from 30 fpm to 105 fpm.
6. The apparatus can tie products from conveyors with any flight spacing, variable spacing, or no flights at all.
7. The apparatus can tie products at varying conveyor speeds, with the mere setting of a switch.
8. The apparatus is manufactured with long-wearing, rust and corrosion resistant materials and components, and with a minimum of moving parts. The result is virtually no maintenance.
The apparatus for applying twist ties of the present invention differs from the similar apparatus disclosed in the above-identified Knudsen patent in three fundamental aspects. First, all of the operations of the apparatus of the present invention are under control of the PLC.
Second, rather than using the gear train of the Knudsen device to transfer motion from the drive motor to the various drive shafts and to control the timing of the several components of each operating cycle, the apparatus of the present invention utilizes a drive train comprising a drive motor, a drive pulley driven by the drive motor, a drive belt driven by the drive pulley, and three driven pulleys each continuously operated under the action of the drive motor, the drive pulley, and the drive belt. A partial revolution clutch is associated with each of the driven pulleys and functions upon actuation by the PLC to connect the drive shafts of the pusher pad assembly, the needle assembly, and the twister hook assembly, respectively, to their respective driven pulleys for actuation thereby.
Third, the apparatus for applying twist ties of the present invention employs photosensors to detect the presence of unwrapped product (such apparatus being referred to as the "naked loaf" detector) and to detect the presence of foreign objects in the area of the twister hook at a time in the operating cycle of the apparatus when no foreign objects should be present in such area to determine fault conditions. Upon determination of any such fault condition, the PLC functions not only to terminate operation of the present apparatus, but also to terminate operation of the associated conveyors and product bagging apparatus, thereby preventing the excessive loss of product which has sometimes been characteristic of the use of prior art apparatus.